The government requires the burning of all excess gases being admitted to the atmosphere. The collection of these gases is normally put into a flare line which is equipped with a pilot light to ensure the burning of all gases.
Recent regulations require that this burning be smokeless in order to reduce air pollution and to be quieter to reduce noise pollution.
In order to keep a flare smokeless, as a steam aspirating gas flare for example, the relative amount of steam used to draw in air for mixing with the gas must be increased greatly as the average molecular weight of the hydrocarbon increases. Accordingly in operation, it has been necessary to set the steam-to-gas ratio high in order to maintain the flare smokeless when the highest molecular weight gas is being supplied to the flare. Thus when a low molecular weight material, such as low purity hydrogen is going to the flare, the flare is noisy due to the roar of the steam jet in the aspirating flare nozzle. It often can be heard from 2 to 10 miles away.